The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Moving Picture Experts Group (MPEG) and Video Coding Experts Group (VCEG) have developed an improved and excellent video compression technology over prior MPEG-4 Part 2 and H.263 standards. The new standard is called H.264/AVC (Advanced Video Coding) and was released simultaneously as MPEG-4 Part 10 AVC and ITU-T Recommendation H.264. H.264/AVC (shortened as H.264 hereinafter) differently uses a spatial predictive coding method relative to existing video coding-related international standards of MPEG-1, MPEG-2, MPEG-4 Part2 Visual, etc.
Conventional methods use “intra prediction” for coefficients transformed in Discrete Cosine Transform Domain (or DCT Transform Domain) to seek higher encoding efficiency resulting in degradation of the subjective video quality at low band transmission bit rates. In contrast, H.264 adopts the method of encoding based on a spatial intra prediction in a spatial domain rather than in a transform domain.
Encoders using an encoding method based on the conventional spatial intra predictions take information on the previously encoded and reconstructed block to predict current block information therefrom, encode information on just the difference of the predicted block from the original block to be encoded, and transmit the encoded information to a decoder. At this time, the encoder may transmit parameters needed for prediction of the block information to the decoder, or the encoder and decoder may be synchronized so that they share the needed parameters for the decoder to predict the block information. On the other hand, the desired block to be currently decoded is generated and reconstructed by first predicting its neighboring blocks that are completely decoded and reconstructed and then obtaining the sum of difference information or residual data transmitted from the encoder and the predicted neighboring block information. Then, also, if the parameters needed for the prediction are transmitted from the encoder, the decoder uses the same to predict the neighboring block information.
There are different intra predictions such as an intra—4×4 prediction, intra—16×16 prediction, and intra—8×8 prediction among others, where the respective intra predictions include a plurality of prediction modes.
FIG. 1 is a exemplary diagram showing conventional nine 4×4 intra prediction modes.
Referring to FIG. 1, the intra—4×4 prediction has nine prediction modes which include a vertical mode, horizontal mode, direct current (DC) mode, diagonal down-left mode, diagonal down-right mode, vertical-right mode, horizontal-down mode, vertical-left mode and horizontal-up mode.
FIG. 2 is an exemplary diagram showing conventional four 16×16 intra prediction modes.
Referring to FIG. 2, the intra—16×16 prediction has four prediction modes which include a vertical mode, horizontal mode, DC mode and plane mode. The intra—8×8 prediction also has four modes similar to the intra—16×16 prediction.
In an intra prediction that uses the DC mode as the prediction mode (or in a ‘DC mode prediction’ in short), the result is an average value obtained in a unit of block. Here, the average value means an average of 8 pixels (for the case of intra—4×4 prediction) from the current block's left side 4 pixels plus the current block's upper side 4 pixels or an average of 32 pixels (for the case of intra—16×16 prediction) from the current block's left side 16 pixels plus the current block's upper side 16 pixels. Therefore, in performing the DC mode prediction, the neighboring blocks to the current block are averaged for predicting all of the 4×4 pixels or the 16×16 pixels.
Hence, regardless of the type of prediction which is intra—4×4 prediction or intra—16×16 prediction or another, the prediction values or predictors are the same with respect to the current block's 16 pixels for the case of intra—4×4 prediction or 256 pixels for the case of intra—16×16 prediction. This lowers the accuracy of predicting the current block to cause a decrease of coding efficiency or compression efficiency.
In addition, the dropped prediction accuracy will increase the differential value between the original block and the predicted block whereby the above DC mode prediction produces a greater amount of the difference information and a decline in the video compression efficiency disadvantageously.